An auxiliary inverter is one of power units of a motor train unit, serves for providing stable three-phase AC and single-phase AC power supplies, and supplies power for an air condition compressor, a ventilation device, an air compressor, an electric heater and a charging set or the like in the motor train unit. Currently, the auxiliary inverter of the motor train unit has three power supply modes: separately supplied power by an inverter power supply, parallel power supply in the absence of interconnecting lines, and parallel power supply in the presence of interconnecting lines. The power supply mode of separately supplied power by an inverter power supply is characterized by simple wiring, larger capacity per unit, and lower reliability because when a single unit breaks down, an adjacent one is needed to be switched to supply power by means of a contactor.
The power supply mode of parallel power supply in the absence of interconnecting lines is characterized in that a control strategy used in generator synchronization is used for reference, the droop method is used, each module only detects the output power of the module itself, and adjusts, after the output power is decomposed into active power and reactive power, an output voltage and frequency of the module according to a certain algorithm to implement current sharing, but the current sharing effect is unsatisfactory, and low-power parallel load generates larger circular current.
The power supply mode of parallel power supply in the presence of interconnecting lines is characterized in that various output modules are in parallel connection, various modules exchange information by means of interconnecting lines to learn the average power or output current of the system, and various modules collect and follow up a shared reference signal to implement a parallel control. This method may significantly improve the current sharing effect and increase reliability and redundancy of the auxiliary power supply system of the motor train unit. However, due to more parallel lines and unstable long-distance transmission signal, the existing parallel power supply system in the presence of interconnecting lines is easy of control error and parallel connection failure. Compared with a photovoltaic grid-connected system and a wind power integration system, a microgrid parallel control system has larger circular current under a low-power parallel load.